Cardiac Magnetic Resonance Imaging in Appraising Myocardial Strain and Biomechanics: A Current Overview.

Subclinical alterations in myocardial structure and function occur early during the natural disease course. In contrast, clinically overt signs and symptoms occur during late phases, being associated with worse outcomes. Identification of such subclinical changes is critical for timely diagnosis and accurate management. Hence, implementing cost-effective imaging techniques with accuracy and reproducibility may improve long-term prognosis. A growing body of evidence supports using cardiac magnetic resonance (CMR) to quantify deformation parameters. Tissue-tagging (TT-CMR) and feature-tracking CMR (FT-CMR) can measure longitudinal, circumferential, and radial strains and recent research emphasize their diagnostic and prognostic roles in ischemic heart disease and primary myocardial illnesses. Additionally, these methods can accurately determine LV wringing and functional dynamic geometry parameters, such as LV torsion, twist/untwist, LV sphericity index, and long-axis strain, and several studies have proved their utility in prognostic prediction in various cardiovascular patients. More recently, few yet important studies have suggested the superiority of fast strain-encoded imaging CMR-derived myocardial strain in terms of accuracy and significantly reduced acquisition time, however, more studies need to be carried out to establish its clinical impact. Herein, the current review aims to provide an overview of currently available data regarding the role of CMR in evaluating myocardial strain and biomechanics.

Left Ventricular Twist Mechanics Are Impaired in Patients with Coronary Slow Flow.

PURPOSE: Coronary slow flow (CSF) is a rare condition described as the delayed angiographic passage of a contrast agent in the absence of stenosis in epicardial coronary arteries. Left ventricular (LV) systolic and diastolic dysfunctions have been described in the presence of CSF. However, the effect of CSF on LV twist functions has not been assessed. We aimed to evaluate the effects of CSF on LV twist mechanics using speckle tracking echocardiography (STE). METHODS: Twenty CSF patients (24-60 years) were enrolled according to the exclusion criteria. Twenty subjects with similar demographic characteristics and normal coronary arteries were the controls. Participants were evaluated with conventional echocardiography and STE. RESULTS: The general characteristics of the two groups were similar. LV twist, LV torsion, and apical rotation were impaired in the CSF group (P = 0.015, P = 0.012, and P < 0.001, respectively). Time to peak twist (TPT) and time to peak untwisting (TPU) were prolonged in CSF patients (P < 0.001 and P < 0.001, respectively). In the CSF group, rotation-deformation delay was shortened (P < 0.001) and global longitudinal strain (GLS) was lower (P < 0.001). The thrombolysis in myocardial infarction (TIMI) frame count was negatively correlated with LV twist, LV torsion and apical rotation (P = 0.002, r = -0.624; P = 0.002, r = -0.624; and P = 0.002, r = -0.632, respectively). CONCLUSIONS: We demonstrated that LV twist mechanics are impaired in CSF patients. Worse LV twist parameters were associated with greater TIMI frame count.